DE2944229A1 - Photographic copy paper exposure calculator - has extreme valve stores assigned to sensors ascertaining lightest and darkest image points - Google Patents

Abstract

The measuring arrangement is for exposure and contrast measuring devices as darkrooms. Two sensors are sequentially switched on to ascertain the lightest and darkest image points. The outputs are fed to two parallel, extreme values stores - one for max. and one for min. A calculator ascertains the mean exposure light intensity or exposure time and the paper grade for best contrast results. This eliminates all subjective evaluation from the photo-laboratory technician. The extreme values can be stored in digital or analogue form. The image points can be measured in any sequence.

Description

description

Paper exposure meter for determining exposure time and amount of copy in one operation The invention relates to paper exposure meters as shown in Photo laboratories to determine exposure time and contrast range (and thus the Paper gradation) can be used.

By adhering to the correct exposure time and (for black and white photography) By choosing the right paper gradation you can achieve optimal photographic quality Magnifications achieved. With the paper exposure meter should be with little Effort, objective and reproducible the correct exposure and gradation values can be determined. The use of suitable paper exposure meters is included considerable time and material savings associated.

With the known paper exposure meters, the exposure measurement takes place either as an integral measurement from the magnifying frame or another Projection surface reflected light or as a point measurement from a point of the projected image from the enlarger.

The integral measurement objectifies the determination of the exposure time by considering a larger area, however, an accurate determination includes the scope of copying.

The point measurement is suitable as a basis for determining the scope of copying, however, it is difficult to determine the exposure time with this method, since it is hardly possible to close the typical pixel right away and without trying Find.

The range of contrast of the image to be enlarged is known from the Devices by measuring the brightness of the brightest and darkest pixel (i.e. from two point measurements). The brightness ratio is thereby through a calibration measurement determines the actuation of one or more operating elements makes necessary.

Koch, Alte Bleiche89, 7920 Heidenheim, 'OPaper exposure meter " Description, page 2 Finding the brightest and darkest pixel remains Left to the subjective perception of the laboratory technician, i.e. the contrast is turned off determined the pixels that the laboratory technician considers to be the extremes of brightness. Want one works with the actual brightness extremes, so is with the known devices time-consuming trial and error required.

The invention is as follows. The task is based on: - The Exposure time should be determined automatically from two pixels. These Image points should be the extremes of brightness, whereby according to Vieth (measuring method der Fotografie, Oldenbourg Verlag Munich 1974) good exposure results can be expected was.

- Finding the Helligkejextrema should be objectified. A way should be found to reduce the brightness extremes without tedious Try to determine.

- The required number of copies of the photo paper should be at the same time can be determined with the exposure time. The determination of the scope of copying should - compared to the determination of the exposure time - no further operating measures require.

The device was designed so that the light measurement by point measurement he follows. For the measurement, a sensor is placed over the (on the magnifying frame or similar) projected image is moving. The brightness values recorded by the sensor are displayed in electrical voltage values implemented. These values are then transferred to a. Maximum and a minimum value memory.

During the measurement, the sensor must also be guided over the extremes of brightness but since the measured extrema are saved in parallel, it is beler, glos, when the sensor is moved over the extremes during a measurement.

Koch, Alte Bleiche 89, 7920 Heidenheim. "Paper light meter" Description. Page3 After the measurement has been completed, stored extreme values are used the mean illuminance (geometric mean of the extreme values) and the range of contrast of the image is calculated.

The calculation is carried out as follows: Both stored extreme values are logarithmized.

The sum of the logarithms is obtained after exponentiation a signal that is proportional to the mean illuminance and the exposure time is reversed proportional. This signal is at the output of the exponentiator P1 (see Picture 1) too.

The difference between three logarithms gives a signal that corresponds to the logarithmic Contrasting scope of the image and thus the logarithmic copying scope of the required Photo paper is proportional. This signal is at the output of the subtracter G2 (Picture 1).

In this description it has been assumed so far that the The copying range of the photo paper should be the same as the contrast range of the picture. Want Sometimes recommended in the literature - if you deviate from this rule, you can Add or subtract the required correction factor at G2 (not shown in Figure 1) The paper exposure meter knows, as far as the memory and arithmetic part is concerned, that Operating phases "measuring" and "computing".

The "measuring" operating phase is characterized by the fact that b4 is actuated and b5 is in the MEASURE position. At the beginning of the measuring phase, the extreme value memories deleted, then the memories are released for the recording of new values. If b4 is no longer actuated, the device goes into the "Calculate" phase. In this During the 2nd phase, the memory inputs are blocked for recording new values respectively.

mean illuminance and logarithmic copying range calculated in this phase as described above. The position is in the calculation phase before b5 irrelevant.

Koch, Alte Bleiche 89, 7920 Heibenheim. "Paper exposure meter" Description, page @ For the sake of completeness, it should be mentioned that in Fig. 1 device shown in the "Measure" phase, ongoing calculations based on the stored values can be carried out. The calculation results obtained in this phase are, however, for the actual determination of exposure time and paper gradation irrelevant.

Let the measured contrast range be kept continuously during the measurement phase display, one can conclude from an increase in the displayed value that that a new extreme value has been detected. If the displayed value no longer increases, then If the measuring process is carried out sensibly, one can expect that the actual Brightness extremes were recorded in the measurement.

Measurement methods and analog solutions have been described above. Of course the signal sent by the sensor can also be digitized and in a digital circuit, which functionally corresponds to the analog circuit shown in Figure 1 will. This digital circuit can be in the form of an individual circuit or as a Computer be implemented with appropriate software.

Advantages of the device described are: - Determination of the exposure time from the extremes of brightness.

that means objectification of the measurement in relation to the exposure it determination from one point.

- The determination of the contrast range from the actual brightness extremes is made much easier and faster, since Fenlveeruche does not start over the measurement.

- Determination of exposure time and gradation solely through the light measurement. Special measures that require time and skill are not taken during the measurement more eeforderloch. The measuring process is accelerated.

Due to the aforementioned advantages - compared A cook, Alte Bleiche 89, 7920 Heidenheim, "Papierbelichtunsmesser" description, page 5 with previous devices - a quality improvement of the created enlargements, combined with time and material savings, which has been proven in practical tests became.

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Claims (6)

Claims S measuring arrangement for exposure and contrast measuring devices characterized by the series connection of sensors, two parallel extreme value memories (one each for maximum and minimum) and computing device for calculating average Illuminance or exposure time and required scope of copying. 2. Measuring arrangement according to 1 in analog technology characterized by analog Storage of extreme values and analog execution of arithmetic operations. 7. Arrangement according to 2 in digital technology characterized by digital Storage of extreme values and digital execution of the arithmetic operations. The digital Realization can take place by means of an individual circuit or with a computer. 4. Measurement methods for exposure and contrast meters marked through simultaneous or quasi-simultaneous determination of exposure time or average illuminance and required scope of copying from the cellularity stream. 5. Method according to 4 gekennæeichnet in that the pixels in can be measured in any order. 6. Arrangement according to 1, characterized in that for the contrast measurement no more operations need to be carried out than for the exposure measurement are required anyway. In particular, no adjustments, potentiometer controls or the like have to be carried out. be performed.